ccna exploration routing chapter 9
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© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicITE PC v4.0Chapter 1 1
EIGRP
Routing Protocols and Concepts – Chapter 9
ITE PC v4.0Chapter 1 2© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Objectives Describe the background and history of Enhanced
Interior Gateway Routing Protocol (EIGRP).
Examine the basic EIGRP configuration commands and identify their purposes.
Calculate the composite metric used by EIGRP.
Describe the concepts and operation of DUAL.
Describe the uses of additional configuration commands in EIGRP.
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Introduction
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EIGRP
Roots of EIGRP: IGRP-Developed in 1985 to overcome RIPv1’s limited hop count
-Distance vector routing protocol
-Metrics used by IGRP
bandwidth (used by default)
Delay (used by default)
reliability
load
-Discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)S
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EIGRP
EIGRP Message Format
EIGRP HeaderData link frame header - contains source and destination MAC address
IP packet header - contains source & destination IP address
EIGRP packet header - contains AS number
Type/Length/Field - data portion of EIGRP message
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EIGRP
EIGRP packet header contains
–Opcode field
–Autonomous System number
EIGRP Parameters contains–Weights
–Hold time
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EIGRP
TLV: IP internal contains–Metric field
–Subnet mask field
–Destination field
TLV: IP external contains–Fields used when external
routes are imported into
EIGRP routing process
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EIGRPProtocol Dependent
Modules (PDM)
EIGRP uses PDM to route several different protocols i.e. IP, IPX & AppleTalk
PDMs are responsible for the specific routing task for each network layer protocol
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EIGRPReliable Transport Protocol (RTP)
Purpose of RTP
–Used by EIGRP to transmit and receive EIGRP packets
Characteristics of RTP
–Involves both reliable & unreliable delivery of EIGRP packet
Reliable delivery requires acknowledgment from destination
Unreliable delivery does not require an acknowledgement from destination
–Packets can be sent
Unicast
Multicast
–Using address 224.0.0.10
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EIGRPEIGRP’s 5 Packet Types
Hello packets–Used to discover & form adjacencies with neighbors
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EIGRP
Update packets–Used to propagate routing information
Acknowledgement packets
–Used to acknowledge receipt of update, query & reply packets
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EIGRP Query & Reply packets
Used by DUAL for searching for networks
Query packets
-Can use
Unicast
Multicast
Reply packet
-Use only
unicast
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EIGRP Purpose of Hello Protocol
–To discover & establish adjacencies with neighbor routers
Characteristics of hello protocol–Time interval for sending hello packet
Most networks it is every 5 secondsMultipoint non broadcast multi-access networks
–Unicast every 60 seconds-Holdtime
This is the maximum time router should wait before declaring a neighbor down
Default holdtime
–3 times hello interval
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EIGRPEIGRP Bounded Updates
EIGRP only sends update when there is a change in route status
Partial update–A partial update includes only the route information that has changed – the whole routing table is NOT sent
Bounded update–When a route changes, only those devices that are impacted will be notified of the change
EIGRP’s use of partial bounded updates minimizes use of bandwidth
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EIGRP
Diffusing Update Algorithm (DUAL)–Purpose
•EIGRP’s primary method for preventing routing loops
–Advantage of using DUAL
•Provides for fast convergence time by keeping a list of loop-free backup routes
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EIGRP
Administrative Distance (AD)–Defined as the trustworthiness of the source route
EIGRP default administrative distances–Summary routes = 5
–Internal routes = 90
–Imported routes = 170
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EIGRP
Authentication
EIGRP can– Encrypt routing information
– Authenticate routing information
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EIGRP
Network Topology
Topology used is the same as previous chapters with the addition of an ISP router
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EIGRP
EIGRP will automatically summarize routes at classful boundaries
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Basic EIGRP Configuration Autonomous System (AS) & Process IDs
–This is a collection of networks under the control of a single authority (reference RFC 1930)
–AS Numbers are assigned by IANA
–Entities needing AS numbers
ISP
Internet Backbone prodiers
Institutions connecting to other institutions using AS numbers
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Basic EIGRP Configuration EIGRP autonomous system
number actually functions as a process ID
Process ID represents an instance of the routing protocol running on a router
Example
Router(config)#router
eigrp autonomous-system
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Basic EIGRP Configuration
The router eigrp command
The global command that enables eigrp is
router eigrp autonomous-system
-All routers in the EIGRP routing domain must use the same process ID number (autonomous-system number)
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Basic EIGRP Configuration
The Network Command
Functions of the network command–Enables interfaces to transmit & receive EIGRP updates
–Includes network or subnet in EIGRP updates
Example–Router(config-router)#network network-address
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Basic EIGRP Configuration The network Command with a Wildcard Mask
-This option is used when you want to configure EIGRP to advertise specific subnets
-Example
Router(config-router)#network network-address [wildcard-mask]
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Basic EIGRP ConfigurationVerifying EIGRP
EIGRP routers must establish adjacencies with their neighbors before any updates can be sent or received
Command used to view neighbor table and verify that EIGRP has established adjacencies with neighbors is
show ip eigrp neighbors
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EIGRP
The show ip protocols command is also used to verify that EIGRP is enabled
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Basic EIGRP Configuration
Examining the Routing Table
The show ip route command is also used to verify EIGRP
EIGRP routes are denoted in a routing table by the letter “D”
By default , EIGRP automatically summarizes routes at major network boundary
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Basic EIGRP Configuration Introducing the Null0 Summary Route
–Null0 is not a physical interface
–In the routing table summary routes are sourced from Null0
Reason: routes are used for advertisement purposes
–EIGRP will automatically include a null0 summary route as child route when 2 conditions are met
At least one subnet is learned via EIGRP
Automatic summarization is enabled
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Basic EIGRP Configuration
R3’s routing table shows that the 172.16.0.0/16 network is automatically summarized by R1 & R3
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EIGRP Metric CalculationEIGRP Composite Metric & the K Values EIGRP uses the following values in its composite
metric-Bandwidth, delay, reliability, and load
The composite metric used by EIGRP– formula used has values K1 K5
K1 & K3 = 1all other K values = 0
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EIGRP Metric Calculation Use the sh ip protocols command to verify the K
values
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EIGRP Metric Calculation
EIGRP Metrics
Use the show interfaces command to view metrics
EIGRP MetricsBandwidth – EIGRP uses a static bandwidth to calculate metric
Most serial interfaces use a default bandwidth value of 1.544Mbos (T1)
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EIGRP Metric CalculationEIGRP Metrics
Delay is the defined as the measure of time it takes for a packet to traverse a route
-it is a static value based on link type to which interface is connected
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EIGRP Metric Calculation Reliability (not a default EIGRP metric)
-A measure of the likelihood that a link will fail
-Measure dynamically & expressed as a fraction of 255
the higher the fraction the better the reliability
Load (not a default EIGRP metric)– A number that reflects how much traffic is using a link
– Number is determined dynamically and is expressed as a fraction of 255
The lower the fraction the less the load on the link
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EIGRP Metric Calculation
Using the Bandwidth Command
Modifying the interface bandwidth-Use the bandwidth command
-Example
Router(config-if)#bandwidth kilobits
Verifying bandwidth –Use the show interface command
Note – bandwidth command
does not change the
link’s physical
bandwidth
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EIGRP Metric Calculation
The EIGRP metric can be determined by examining the
bandwidth delay
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EIGRP Metric Calculation
EIGRP uses the lowest bandwidth (BW)in its metric calculation
Calculated BW = reference BW / lowest BW(kbps)
Delay – EIGRP uses the cumulative sum of all outgoing interfaces
Calculated Delay = the sum of outgoing interface delays
EIGRP Metric = calculated BW + calculated delay
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EIGRP Metric Calculation
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DUAL Concepts
The Diffusing Update Algorithm (DUAL) is used to prevent looping
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DUAL Concepts
Successor
The best least cost route to a destination found in the routing table
Feasible distance
The lowest calculated metric along a path to a destination network
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DUAL Concepts
Feasible Successors, Feasibility Condition & Reported Distance
Feasible Successor
-This is a loop free backup route to same
destination as successor route
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DUAL Concepts
Reported distance (RD)
-The metric that a router reports to a neighbor about its own cost to that network
Feasible Successors, Feasibility Condition & Reported Distance
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DUAL Concepts
Feasibility Condition (FC)
-Met when a neighbor’s RD is less than the local router’s FD to the same destination network
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DUAL Concepts
Topology Table: Successor & Feasible Successor
EIGRP Topology table–Viewed using the show ip eigrp topology command
Contents of table include:
– all successor routes
– all feasible successor routes
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DUAL Concepts
EIGRP Topology Table dissected
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DUAL ConceptsTopology Table: No
Feasible Successor
A feasible successor may not be present because the feasibility condition may not be met
-In other words, the reported distance of the neighbor is greater than or equal to the current feasible distance
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DUAL Concepts
Finite Sate Machine (FSM)
–An abstract machine that defines a set of possible states something can go through, what event causes those states and what events result form those states
–FSMs are used to describe how a device, computer program, or routing algorithm will react to a set of input events
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DUAL Concepts
DUAL FSM
–Selects a best loop-free path to a destination
–Selects alternate routes by using information in EIGRP tables
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DUAL Concepts
Finite State Machines (FSM)
To examine output from EIGRP’s finite state machine us the debug eigrp fsm command
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More EIGRP Configurations
The Null0 Summary Route
By default, EIGRP uses the Null0 interface to discard any packets that match the parent route but do not match any of the child routes
EIGRP automatically includes a null0 summary route as a child route whenever both of the following conditions exist
–One or subnets exists that was learned via EIGRP
–Automatic summarization is enabled
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More EIGRP Configurations
The Null0 Summary Route
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More EIGRP Configurations
Disabling Automatic Summarization
The auto-summary command permits EIGRP to automatically summarize at major network boundaries
The no auto-summary command is used to disable automatic summarization
–This causes all EIGRP neighbors to send updates that will not be automatically summarized
this will cause changes to appear in both
-routing tables
-topology tables
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More EIGRP Configurations
Manual Summarization
Manual summarization can include supernetsReason: EIGRP is a classless routing protocol & include subnet mask in update
Command used to configure manual summarization –Router(config-if)#ip summary-address eigrp as-number
network-address subnet-mask
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More EIGRP Configurations Configuring a summary route in EIGRP
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More EIGRP Configurations
EIGRP Default Routes
“quad zero” static default route
-Can be used with any currently supported routing protocol
-Is usually configured on a router that is connected a network outside the EIGRP domain
EIGRP & the “Quad zero” static default route
–Requires the use of the redistribute static command to disseminate default route in EIGRP updates
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More EIGRP Configurations
Fine-Tuning EIGRP
EIGRP bandwidth utilization-By default, EIGRP uses only up to 50% of interface bandwidth for EIGRP information
-The command to change the percentage of bandwidth used by EIGRP is
Router(config-if)#ip bandwidth-percent eigrp as-number percent
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More EIGRP Configurations Configuring Hello Intervals and Hold Times
-Hello intervals and hold times are configurable on a per-interface basis
-The command to configure hello interval is
Router(config-if)#ip hello-interval eigrp as-number seconds
Changing the hello interval also requires changing the hold time to a value greater than or equal to the hello interval
-The command to configure hold time value is
Router(config-if)#ip hold-time eigrp as-number seconds
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Summary Background & History
–EIGRP is a derivative of IGRP
EIGRP is a Cisco proprietary distance vector routing protocol released in 1994
EIGRP terms and characteristics–EIGPR uses RTP to transmit & receive EIGRP packets
–EIGRP has 5 packet type:
Hello packets
Update packets
Acknowledgement packets
Query packets
Reply packets
–Supports VLSM & CIDR
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Summary
EIGRP terms and characteristics
–EIGRP uses a hello protocol
Purpose of hello protocol is to discover & establish adjacencies
–EIGRP routing updates
Aperiodic
Partial and bounded
Fast convergence
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Summary
EIGRP commands–The following commands are used for EIGRP configuration
RtrA(config)#router eigrp [autonomous-system #]RtrA(config-router)#network network-number
–The following commands can be used to verify EIGRPShow ip protocolsShow ip eigrp neighborsShow ip route
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Summary
EIGRP metrics include
–Bandwidth (default)
–Delay (default)
–Reliability
–Load
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Summary DUAL
–Purpose of DUALTo prevent routing loops
–SuccessorPrimary route to a destination
–Feasible successorBackup route to a destination
–Feasible distanceLowest calculated metric to a destination
–Reported distanceThe distance towards a destination as advertised by an upstream neighbor
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Summary Choosing the best route
–After router has received all updates from directly connected neighbors, it can calculate its DUAL
1st metric is calculated for each route
2nd route with lowest metric is designated successor & is placed in routing table
3rd feasible successor is found
–Criteria for feasible successor: it must have lower reported distance to the destination than the installed route’s feasible distance
–Feasible routes are maintained in topology table
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Summary
Automatic summarization
–On by default
–Summarizes routes on classful boundary
–Summarization can be disabled using the following command
RtrA(config-if)#no auto-summary
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